In an industrial culture, oxygen necessary for biomass to grow in a culture medium containing nutrient components such as glucose and glutamine is supplied in a form of a bubble aerating gas or supplied by aeration onto a liquid free surface while the culture medium is often frequently stirred to grow the biomass, harvesting a responsible material produced by the biomass. To successfully achieve biomass culture, it is required that inner fermenter conditions suitable for biomass culture be secured. In contrast, the structure and running conditions of the fermenter contribute to deviation from these suitable inner fermenter conditions.
To ensure an increased volumetric mass transfer coefficient kLa for oxygen in the fermenter, and homogeneous mixture of the nutrient components and a dissolved oxygen concentration, the culture medium is stirred by impellers. Is difficult to achieve high kLa and sufficient homogeneity as for high-viscosity culture media. Though an attempt has been made to experimentally obtain the volumetric oxygen transfer coefficient kLa for each type of fermenter, in such an experimental method (Japanese Patent Publication (Kokai) No. 2001-231544), kLa varies with the tank diameter of the fermenter, the diameter of bubbles, the diameter of impellers, and the rotation speed and consistently depends on the type of fermenter. Therefore, this method lacks generality. In the case where aeration onto the liquid free surface and aerating into the culture medium are combined, the ratio between both two depends on the conditions, making it difficult to obtain general knowledge. To enhance an increase in kLa and the homogeneity, the rotation speed of the impellers may be increased, though usually, agitation power constraints it. In culturing the mammalian cells, such a problem arise that to strong agitation may bring the cells to death. To avoid experimental constraints, an attempt has been made to use fluid numeric simulation in designing the fermenter structure (Japanese Patent Publication (Kokai) No. 2001-75947), which has provided no knowledge of a fluid field suitable for biomass growth. No method for applying fluid numeric simulation to control has been established.
Any starvation of nutrient components in the culture process inhibits growth of the biomass. In many cases, the components such a lactate, ammonia, and alcohol produced as by-products suppress the growth of the biomass, deteriorating the yield of responsible products. Accordingly, it is always important to measure the components in the culture medium and to sustain the nutrient components during fermenter's running. However, no satisfactory technique has been established for reflecting the measurement results in fermenter control. An attempt has been made to make a model of a biomass growing process by a differential equation of reaction dynamics, though no computer-aided control method, which combines both the techniques for modeling of the biomass growing process and achieving of hydrodynamic conditions in the fermenter, has been reported.